Hello,
Where can I find the Main Computer in the S90 ?
How ofter do they Fail ?

Thank You ..!

 

They don't fail often. I think it's under the passenger side dash.

 

I found it RSPI..!, thank you.. BTW i have a new one coming, will replace and will post results.

 

The main Computer "ECU" and the Transmission Computer is located on the left side, driver's side, right under the hood-release handle panel. Very easy to find and easy access.
If you need to replace it, make sure you know the serial number; this tells you the date it was manufactured. Do not buy one that is older than yours; The 960 1990 to 1996 which looks like the S90 shares shares some of the same parts.



1998 S90

 

Cool. Did things work out for you?

 

Unfortunately No..!
I should have listened to you, “ Might also be a good idea to do a compression test. “
I should have done the compression test first; all well.. I’ve learned a lot.
Compression on Cyl #4 and #5 was 65psi when hot; needless to say I am running on 4 now.
This is all I have replaced, Ignition coils, injectors, aux secondary air pump, cam position sensor, spark plugs, ignition modules and finally the ECM. .. plus all my labor.
After all these, it leads me to believe that I have one or more bad valves or bad cyl rings.
I can’t spend anymore on this thing…162K it’s time to get another one.

Thank you Very much RSPI.

 

Sorry to hear that you did not find the problem. What was your initial symptoms? Did you have codes for them?

 

I think I found the original post: https://volvoforums.com/forum/volvo-s90-v90-40/4-5-cyl-misfiring-45249/

That is strange that the compression test was fine and now is bad. Not sure how that happened.

 

My bad, the first comp test was performed while engine was cold/warm and did not run engine long enough for the comp test gauge to give me a good reading; a good 25 seconds is enough. Lesson learned, perform this test at a hot/running temp.
With Cyl #4 and #5 reading only 65psi, it leads me to believe that it's a head gasket, what do you think ?

 

Way above my head on that one. I'd have to start some reasearch and I won't have time for that for a couple of weeks.